I never really understood why not simply use milliseconds since the epoch and keep track of a time zone separately if needed... This allows fairly easy conversion to most native systems i have worked with, easy sorting and diff operations as well as final display control. Also don't have a need to be thinking about daylight savings then, or do other conversions for say timesheets.
It depends on what you need to do. If you just need to say when something happened (e.g. some log event) then milliseconds since the epoch is fine. If want a user to schedule a reoccurring meeting at 8am on the first Thursday of every month, you can also keep a set of timestamps as milliseconds since the epoch, but you are going to need to do some work to figure out the right numbers correctly.
> If want a user to schedule a reoccurring meeting at 8am on the first Thursday of every month, you can also keep a set of timestamps as milliseconds since the epoch
No, you can't really, especially if the recurring meetings go on more than a few years into the future. If the time zone rules themselves change (e.g. if the user's country abolishes or introduces DST), then the timestamps you stored will become wrong in light of the change.